Preparing for future lunar exploration makes it imperative to understand the effects of lunar dust on human and mechanical systems. Lunar dust (including that part of the lunar regolith less than 20 μm in diameter) was found to produce several problems with mechanical equipment and could have conceivably produced harmful physiological effects for the astronauts.
For instance, the abrasive nature of the dust was found to cause malfunctions of various joints and seals of the spacecraft and space suits. Additionally, though efforts were made to exclude lunar dust from the cabin of the lunar module, a significant amount of material nonetheless found its way inside. With the loss of gravity, correlated with ascent from the lunar surface, much of the finer fraction of this lunar dust began to float within the cabin and was inhaled by the astronauts.
Therefore, because lunar dust is to be inevitably encountered, it is necessary for studies to be carried out in a variety of disciplines to mitigate the effects of the lunar dust as completely as possible. As such, understanding the physics, chemistry, and toxicity of lunar dust in the lunar environment is essential for current and future lunar exploration.
Several hundred kilograms of lunar soil and rocks were recovered from the numerous moon missions and returned to earth. However, the quantity of lunar dust brought back could never be enough to satisfy the many tests and developments that require its use and study. Therefore, in order to do research on and study the effects of lunar dust, several simulants have been produced to mimic actual lunar dust.
It must be noted, however, that actual lunar dust contains chemically reactive iron nanoparticles, for which no lunar dust simulant has been able to replicate. Therefore, given the extreme environment in which astronauts and their systems operate and the need for those systems to act in a predictable fashion, it is imperative that a lunar dust simulant be created that as closely resembles actual lunar dust as possible.
The synthesis of iron nanoparticles in carbon has been performed previously by Applicant in 1994 and was reported in an article entitled: Ferric Chloride-Graphite Intercalation Compounds Prepared From Graphite Fluoride. Carbon, vol. 33, no. 3, 1995, pp. 315-322; and in an article entitled: Fabrication of Iron-Containing Carbon Materials From Graphite Fluoride. NASA TM-107133, 1996. The chemical process includes exposing a mixture of ferric chloride (FeCl3) and graphite fluoride (CFx) at a temperature at or between 200° C. and 400° C., followed by oxidation at a temperature at or between 600° C. and 700° C., and reduction at a temperature at or between 800° C. and 1200° C. The chemical equation for this reaction is described as reaction (1):
where C(XX) means nanoparticles of XX embedded in carbon.
As shown in FIG. 1, the stability of this product was examined by comparing its x-ray diffraction (XRD) data taken 1 week, 1 year, and 14 years after it was produced, adhered to a glass slide by double-sided adhesive tape and stored in ambient air. This particular sample, C(Fe, FeO, Fe3O4), was made according to the above-described reaction (1), where the final reduction did not reach completion. The 1-year and 14-year data points were taken from the same instrument at the same setting. From these XRD data, no oxidation of the α-iron nanoparticles can be observed during this 14-year period, since the Fe2O3 peak continues to be missing, and the FeO and Fe3O4 peak height relative to the Fe peak became lower as time progressed. This suggests the iron nanoparticles were well embedded in carbon and well protected from the surrounding ambient air.
Additionally, the α-iron nanoparticles appear to become either more ordered or larger in size during the 14-year period, as the width of the α-iron's peak, as shown as (110) in FIG. 1, becomes narrower. This sample was not examined by transmission electron microscopy (TEM). However, a TEM image of its precursor, C(FeFyClz), as shown in FIG. 2 shows the particle size was in the <10 to 100 nm range. Other TEM images of this precursor show nanoparticles as large as 250 nm.
It was thought that the trace amount of ambient air in nitrogen could be the source of oxygen from which the FeO and Fe3O4 nanoparticles in reaction (1) are produced. However, trace amounts of air were later found to be insufficient to prevent the iron halide from evaporation. Alternatively, large amounts of air reacted with iron halide quickly to form large Fe2O3 particles separated from the carbon structure.